Solvent-type adhesive agents have been rapidly replaced with water-based adhesive agents in recent years in the field of adhesive agents because the water-based adhesive agents have various advantages over the solvent-type adhesive agents in occupational safety and health problems, environmental concerns, suitability for resource saving, and the like.
As a method of making a curable polymer into an aqueous emulsion, Patent Document 1 discloses a method of producing a curable polymer emulsion including a step (1) in which a solution formed from a hydrolyzable silyl group-containing radical polymerizable monomer, a monomer that can be copolymerized with said monomer, and an oil-soluble radical polymerization initiator is emulsion-dispersed in an aqueous medium containing a surfactant having an HLB of 1.5 to 20 and a pH buffer, and a step (2) in which the aqueous emulsion dispersion obtained in the step (1) is fed continuously or intermittently into an aqueous medium that is being stirred to polymerize the monomers in the medium. However, the method of producing the polymerizable emulsion described in Patent Document 1 requires preparation of an emulsion having a small particle size of the monomer mixture as the aqueous emulsion to be used. Thus, to industrially produce the polymerizable emulsion, problems exist in that a special dispersing device having high shear force is required and that the operation becomes complicated.
Furthermore, Patent Document 2 discloses, as a water-based adhesive composition, a highly water resistant adhesive composition containing a main agent formed from one type or two or more types selected from the group consisting of a water-soluble polymer aqueous solution, an aqueous latex, and an aqueous emulsion, a curing agent formed from an isocyanate compound containing 2,4′-diphenylmethane diisocyanate, and a compound having a specific imide structure. However, the adhesive composition described in Patent Document 2 requires a mixing step because it is a two-part composition, and there are problems such as occurrence of mixing failure.